The present invention relates to a packaging strap coil which is made up of a helically wound thermoplastic resin packaging strap and used in strapping various items, and a method for producing the same. The present invention also relates to a packaging strap coil unit comprising the strap coil, and further relates to a packaging machine equipped with a strap coil reel for loading the strap coil on an automatic packaging machine.
A tape-like thermoplastic resin packaging strap is employed for strapping a corrugated cardboard box or the like. The resin strap is usually manufactured by extrusion-moulding an olefinic thermoplastic resin (i.e. polypropylene, polyethylene terephthalate) into a required flat tape shape, in which case drawing and stretching of the resin is carried out at a rate exceeding the extrusion rate. The stretched resin strap is helically wound up on a tubular paper core to form a strap coil.
The strap coil is loaded on an automatic packaging machine, together with the tubular paper core. A strap therein is successively drawn out to strap a corrugated cardboard box or like item. When the strap coil runs out of the strap, it consists of the tubular paper core. The paper core has been marred by the strap and may not be reused as the core of the packaging strap coil. If the paper core is stained with a synthetic resin-based adhesive, it even fails to make a material for recycled paper. The tubular paper core, which is no longer available as a paper core or a material for recycled paper, is only to be discarded. Disposal of the paper core, however, still requires transportation and waste treating expenses.
In view of the above problems, Japanese Patent Application Laid-open No. 315690/1995 (JP-A-7-315690) discloses a coreless packaging strap coil and a manufacturing method thereof, wherein a packaging strap is helically wound in the absence of a paper or like core. As shown in FIGS. 57 and 58, the coreless strap coil 205 has a cylindrical hollow 206 at its axis. The innermost end of the strap 204 is melt-bonded at a melt-bonded area 241 with another strap layer overlaid on the top side thereof.
To produce this strap coil, a strap 204 is wound on a winding roller 201 comprising a pair of separable right/left roller components 203, 213. Firstly, the start of the strap 204 is wound in one turn along the middle of the axial length of the winding roller 201 where the right/left roller components 203, 213 are joined. Then, the strap 204 provides another layer thereon. The laminated strap layers are melted and bonded to each other by applying a heated iron, thereby forming a melt-bonded area 241. Once the innermost end of the strap 204 is fixed, a predetermined length of the strap 204 is wound on the entire surface of the winding roller 201 to form a strap coil. Finally, the right/left roller components 203, 213 of the winding roller 201 are disjoined and removed from the strap coil. Thus obtained is a coreless packaging strap coil 205.
In this packaging strap coil, the fined innermost end of the strap is not drawn out into the hollow at the axis. Therefore, the strap coil remains firm and solid even during transportation.
When this strap coil is loaded on an automatic packaging machine, the strap is drawn out from the outermost end and used for strapping a corrugated cardboard box or like items.
As mentioned above, a heated iron is used to heat a predetermined area on the laminated portion of the strap wound on the winding roller, so that the laminated strap portion is melted and bonded together. However, as the iron fails to give a stable heating temperature, the bonding strength of the laminated strap layers may vary from batch to batch. Provided the innermost end of the strap is bonded too strongly, namely, provided the melt-bonded area possesses too high a peeling strength, the bonded area may not peel readily when used in the packaging machine. In some cases, the strap may be partially torn off at the rigidly bonded area. Actually, when a strap coil is loaded on the automatic packaging machine, the strap is drawn out along with the rotation of the feed rollers. If the laminated layers of the strap are bonded too strongly, the feed rollers may fail to peel off the strap layers, and worse, destroy themselves, depending on the rotation power.
The strap coil of the prior art manifests more defects. As a strap coil is prepared by laminating a strap in a spiral form, it is somewhat extended in the axial direction. Although the innermost end of the strap is bonded with a layer or layers laminated thereon, the rest of the innermost rows of the strap coil which axially neighbour the bonded strap end are left unbonded with respect to the layers laminated thereon.
Such a strap coil may unwind or collapse at the non-bonded area.
For transportation or storage, the prior art strap coils are laid horizontally and stacked on top of each other as shown in FIG. 55, with the axis oriented vertically. Usually, a pair of strap coils 101 are vertically stored in a package (shown by imaginary line). Each strap coil 101 has uneven side surfaces by nature, where the edge of the strap 101a sticks out in some layers. When a plurality of strap coils 101 are laid axiswise vertically on top of each other, as shown in FIG. 55, the edge of the strap 101a projecting from the side surfaces of the strap coil 101 can be bent or deformed. The strap coil 101 which includes a strap bent or deformed on the edge is less likely to ensure smooth supply of the strap 101a in the automatic packaging machine.
To protect the side surfaces of a strap coil, the strap coil 101 is conventionally transported or stored in the form of a strap coil unit shown in FIG. 56, which includes a pair of disc pads 102 applied on each side surface of the strap coil 101. Each disc pad 102 is made of cardboard and formed with a central hole 102a which corresponds to the cylindrical hollow 101a at the axis of the strap coil 101. A pair of pads 102 are integrally joined on the side surfaces of the strap coil 101 by a plurality of straps 103. Each strap 103 ties the strap coil 101 and the pads 102 together, passing axially through the hollow of the strap coil 101 and the holes of the pads 102 and then axially crossing the outer cylindrical surface of the strap coil 101.
Since the cardboard pads 102 cover both side surfaces of the strap coil 101, the edge of the strap 101a, even if it may unevenly project or sink, is protected from deformation or damage.
Nonetheless, the preparation of such packaging strap coil units is not a simple task, because the process requires positioning the pads 102 on both side surfaces of the strap coil 101 and thereafter tying them together by a plurality of straps 103.
As for an automatic packaging machine equipped with a strap coil reel and operated for packaging an item automatically, the strap coil reel usually accommodates a strap coil comprising a strap wound around a tubular paper core. The strap coil reel includes a core element which is inserted into the paper tube and supports the same. As the core element, there may be adopted a cylindrical structure which comprises a cylinder whose diameter is slightly smaller than the inner diameter of the paper tube, a three-parallel-rod structure in which three parallel rods support the inner cylindrical surface of the paper tube at three circumferentially evenly spaced positions, or a flat-plate structure which comprises a pair of parallel plates. When the core element of the strap coil reel holds a tubular paper core, the strap coil reel is rotated by the inertia force generated while the strap is drawn out from the strap coil by the feed rollers.
Unfortunately, in inserting the core element into the hollow of the coreless strap coil, friction with the core element may induce the strap coil to unwind or disintegrate on the inner cylindrical surface thereof. Besides, this core element is not applicable to a coreless strap coil which has a deformed oval section and thus an oval hollow, which is often observed during and after transportation of the strap coil. If the core element of the strap coil reel cannot be inserted into a deformed hollow, it is impossible to load a deformed strap coil on the strap coil reel.
In fact, if the core element comprises three parallel rods or a pair of flat plates, it can enter a hollow of a strap coil having a slightly deformed oval section. Nevertheless, under such circumstances, the inner cylindrical surface of the strap coil surrounding the deformed hollow cannot receive a circumferentially equally dispersed force. As a result, when the strap coil gets thinner, the hollow of the strap coil may be further deformed into a triangular section or a square section, as loaded on the core element of three-parallel-rod structure or flat-plate structure, respectively. After all, the strap coil reel cannot draw out a strap from the strap coil smoothly.
Moreover, the strap coil reel fails to draw out the strap to the ultimate end for other reasons. Since the rotation of the strap coil reel depends on the inertia force generated in drawing out the strap, the strap constituting the strap coil may bite into the core element and get entangled or disintegrated, when the strap coil becomes thinner. Furthermore, where the strap coil reel is installed on the outside of the automatic packaging machine, there are some possibilities of hurting an operator. When the melt-bonded end in the coreless strap coil is peeled off from the bonded layer, it may violently spring back along with the rotation of the strap coil reel, possibly at an operator.
In order to solve the above problems, the present invention provides a packaging strap coil and a method for producing the same, wherein the innermost end of the strap is firmly fixed to prevent unwinding or disintegration of the strap coil, and further, the strap is smoothly drawn out to the ultimate end when employed for strapping an item.
Another object of the present invention is to provide a packaging strap coil unit, wherein it effectively prevents deformation and bent at the edge of the strap which constitutes the side surfaces of a packaging strap coil comprising a helically wound strap. Besides, this strap coil unit is manufactured in a simple manner.
A further object of the present invention is to provide a packaging machine equipped with a strap coil reel, wherein the coreless strap coil, even if deformed, can be loaded on the strap coil reel without sacrificing its firmly coiled state. With this strap coil reel, a strap can be drawn out safely and stably to the ultimate end.
In view of the above-mentioned objects, the present invention provides a packaging strap coil comprising a number of layers of a packaging strap wound helically and carelessly around a hollow defining an axis of the strap coil, the strap being made of a thermoplastic resin at least on an external surface thereof, wherein a plurality of perforations are pierced in the vicinity of an innermost strap end through to a plurality of strap layers laminated thereon, and wherein the laminated strap layers are bonded to each other at a melt-bonded area formed along the periphery of each perforation. In this packaging strap coil, it is desirable to provide a plurality of perforations pierced in the vicinity of an outermost strap end through to a plurality of strap layers laminated thereunder.
It should be understood that a thermoplastic resin packaging strap employed in the present invention comprises at least a thermoplastic resin. This means that the strap may comprise a thermoplastic resin alone. But, on the other hand, the strap may be made of a fibre, paper, etc. whose surface is coated with a thermoplastic resin.
Moreover, in the packaging strap coil, it is preferable to prescribe the perforation as to the circumferential length, configuration and position thereof as well as the number of laminated strap layers through which the perforation should extend. These parameters are determined in view of the material, thickness and width of the packaging strap. Thereby, the laminated strap layers exhibit a balanced bonding strength and peeling strength.
As described above, the strap coil of the above structure is characterised in that the laminated layers in the vicinity of the innermost strap end are bonded together at the melt-bonded area. The melt-bonded area provides a stable bonding strength and serves as the core of the strap coil. As a result, the strap coil does not unwind or collapse on the inner cylindrical surface. Besides, the strap can be stably laminated on the bonded layers to form a solid strap coil.
When the perforations are provided in the vicinity of an outermost strap end through to a plurality of underlying strap layers, the strap will not unwind from the outermost end. This arrangement thus saves the trouble of fixing the outermost strap end by taping or thermal melt-bonding.
The perforations are judiciously designed to hold the balance between the bonding strength and the peeling strength at the bonded layers of the strap. Therefore, on the one hand, the laminated portion of the strap is mutually bonded with a stable bonding strength at the melt-bonded area formed along the periphery of the perforation. On the other hand, in use of the strap coil, the bonded strap layers peel off properly at the melt-bonded area, instead of being forcibly torn away.
In this connection, the present invention provides a production method of the above strap coil which comprises the steps of:
winding an innermost strap end on a winding roller and laminating a plurality of layers on the innermost strap end;
piercing the laminated strap layers with a perforator heated to a predetermined temperature, thereby to form a perforation and melt its periphery;
withdrawing the perforator from the laminated strap layers to melt-bond the periphery of the perforation;
winding a required length of the strap helically on the winding roller to form a strap coil; and
removing the winding roller from the strap coil.
In the production method, the winding roller may expand or contract diametrically. The diameter of the winding roller is expanded while the strap is wound thereon to form a strap coil. Thereafter, the winding roller is diametrically contracted and removed from the strap coil.
Incidentally, the perforator may be in the form of a needle or a plate.
Further, the present invention provides another method for producing a packaging strap coil comprising the steps of:
winding an innermost strap end on a winding roller and laminating a plurality of layers on the innermost strap end;
irradiating a laser beam on the laminated strap layers, thereby to form a perforation and melt-bond its periphery;
winding a required length of the strap helically on the winding roller to form a strap coil; and
removing the winding roller from the strap coil.
In this production method, too, the winding roller may expand or contract diametrically. The diameter of the winding roller is expanded while the strap is wound thereon to form a strap coil. Thereafter, the winding roller is diametrically contracted and removed from the strap coil.
In any of the above production methods, it is important to prescribe the circumferential length, configuration and position of the perforation as well as the number of laminated layers of the strap through which the perforation should extend. These parameters are determined in view of the material, thickness and width of the packaging strap. Thereby, the laminated strap layers exhibit a balanced bonding strength and peeling strength.
In these production methods, a needle-shaped perforator provides a perforation of circular section, and a plate-shaped perforator provides a perforation of rectangular section or other section corresponding to the section of the perforator. Alternatively, laser beam irradiation can provide a perforation of smaller diameter by removing the components in the irradiation area. In another aspect, compared to the use of needle-shaped or plate-shaped perforators, the laser beam application requires less expendable components.
From another point of view, the present invention provides a strap coil which comprises a number of layers of a packaging strap wound helically and carelessly around a hollow defining an axis of the strap coil, the strap being made of a thermoplastic resin at least on an external surface thereof, wherein a portion of the strap which constitutes an inner cylindrical surface surrounding the hollow is peelably bonded by an adhesive to another portion of the strap.
In this strap coil, the adhesive-bonding can be effected in various manners. For example, a portion of the strap helically wound in the vicinity of the hollow may be peelably bonded by an adhesive to another portion of the strap laminated on a top side thereof.
Otherwise, a plurality of layers of the strap laminated along each axial end of the hollow maybe bonded mutually peelably by an adhesive. Alternatively, a plurality of adjacent rows of the helically wound strap may be bonded mutually peelably by an adhesive which is applied on the inner cylindrical surface surrounding the hollow.
The adhesives for the above embodiments may be solvent-type or hot-melt-type.
Still another method for producing a packaging strap coil comprises the steps of:
winding an innermost strap end helically on a winding roller to form an innermost strap layer;
applying an adhesive on a top side of the strap wound on the winding roller;
winding a required length of the strap helically on the adhesive-applied portion of the strap to form a strap coil; and
removing the winding roller from the strap coil.
In the above production method, the adhesive may be coated by pressing a coating roller of an applicator against the innermost strap layer wound on the winding roller. Instead, the adhesive may be continuously injected between the innermost strap layer wound on the winding roller and a strap which is being laminated thereon, with the use of an applicator which moves along the latter.
Yet another method for producing a packaging strap coil comprises the steps of:
winding an innermost strap end on a winding roller, with applying an adhesive on a plurality of layers of the strap laminated along each axial end of the winding roller;
winding a required length of the strap to form a strap coil; and
removing the winding roller from the strap coil.
Herein, the adhesive can be sprayed on the layers of the strap laminated along each axial end of the winding roller.
Now, the description turns to a packaging strap coil unit of the present invention. The packaging strap coil unit comprises:
a packaging strap coil comprising a packaging strap wound helically and carelessly around a hollow defining the axis of the strap coil, the strap being made of a thermoplastic resin at least on an external surface thereof, and
a pair of disc-shaped pads, concentrically positioned and peelably bonded by an adhesive on each side surface of the strap coil.
In this strap coil unit, each pad may include, in the centre thereof, a plurality of central flaps which are folded into the hollow defining the axis of the strap coil. Desirably, each pad may include, on the outer circumference thereof, a plurality of external flaps which are folded on the outer cylindrical surface of the strap coil.
Another packaging strap coil unit of the present invention comprises: a packaging strap coil comprising a packaging strap wound helically and carelessly around a hollow defining the axis of the strap coil, the strap being made of a thermoplastic resin at least on an external surface thereof; and a shape retention plate for substantially covering the inner cylindrical surface surrounding the hollow. When the shape retention plate is rolled and inserted into the hollow of the strap coil, it is capable of supporting the inner cylindrical surface of the strap coil with a resilient force in an unrolling direction. Preferably, the shape retention plate has a mutually connectable portion at each lengthwise end portion. Further, the shape retention plate may comprise a pair of slits formed in the vicinity of and oriented parallel to one widthwise side, and a pair of extensions projecting from the other widthwise side. When the shape retention plate is rolled and inserted into the hollow, the extensions are fitted in the slits. In addition, the shape retention plate may comprise a plurality of edge pieces provided on each lengthwise side thereof for holding a widthwise edge of the strap coil.
Finally, the description is directed to a packaging machine. The packaging machine of the present invention is equipped with a strap coil reel which accommodates a packaging strap coil comprising a packaging strap wound helically and corelessly around a hollow defining an axis of the strap coil, the strap being made of a thermoplastic resin at least on an external surface thereof. While the packaging machine automatically straps an item, the strap is drawn out along with the rotation of the strap coil. The strap coil reel comprises a core element which can contract diametrically in at least one end thereof so as to be inserted into the hollow of the strap coil, and which can diametrically expand inside the hollow into a circular-section cylindrical shape so as to be pressed against a portion of the strap which constitutes an inner cylindrical surface surrounding the hollow.
For a desirable packaging machine equipped with the strap coil reel, the core element is composed of a plurality of core plates which constitute a cylindrical circumference of the expanded core element, each core plate being displaceable in the radial directions. In this strap coil reel, the core plates may be displaced by a link mechanism or by air pressure.
Furthermore, in the strap coil reel mounted on a desirable packaging machine, the core element may be composed of a plurality of core pieces which together constitute a truncated cone when confronted with each other. The core element of this arrangement can contract diametrically when an extreme end of each core piece comes closer to the other, whereas the core element can expand diametrically when an extreme end of each core piece separates farther away from the other.
The packaging machine of the present invention is advantageously equipped with the strap coil reel as described above. Since the strap coil reel properly tensions the packaging strap, the strap is prevented from biting into the strap coil. Therefore, the strap coil loaded therein is neither deformed in section nor unwound at the inner cylindrical surface. Besides, by designing the core element to contract/expand diametrically (i.e. the diameter of the core element can be reduced and increased), the strap coil reel can be loaded with a deformed eccentric strap coil, while effectively preventing unwinding thereof on the inner cylindrical surface. To be specific, when the core element is diametrically contracted, it can be inserted with respect to the deformed hollow of the strap coil. Thereafter, the core element is diametrically expanded and pressed against the inner cylindrical surface of the strap coil.